Toner is a developer material for a laser printer or a copy. The principle of operation of a printer substantially summarized as follows: a constant current flow through a charging roller to charge the surface of photosensitive drum uniformly. The surface of photosensitive drum which is charged uniformly is exposed with a laser beam and discharged to form an electrostatic latent image. The toner on the surface of the developing roller is charged by the friction of the blade. Under the action of the potential difference, the toner is absorbed on the surface of photosensitive drum to translate the electrostatic latent image to an image. Attracted by the opposite charges of a transfer roller, the image on the surface of photosensitive drum can be transferred on a paper. The image formed by the toner is hot melted and pressurized by a heating roller and a pressure roller. It is fixed on the surface of the paper. Thereby, we will get a printed image.
It can be seen from the running process of the printer that the surface uniformity and stable charging performance of the toner particles play a crucial role and influence in getting the image with a desired printing effect. Of course, the toner should have some other essential properties such as excellent transfer printing property, low-temperature fixation and environmental stability. The toner with a good sphericity has a high transfer printing efficiency, which can be easily transferred and printed from the photosensitive drum to the paper, while reducing or preventing toner remained on the surface of photosensitive drum.
Traditional mechanical pulverizing toner can be obtained by melting and blending resin, CCA, pigment and wax, pulverizing and classifying. The toner particles are irregular in shape. After the friction of the blade, these particles are non-uniformly charged due to the varied surface pressure. Furthermore, the pulverizing process causes some of CCA particles can easily fall off, which also results in the nonuniform charges and wide charges distribution of toner particles. In addition, the pulverizing toner cannot meet the requirements of low-temperature fixation and environmental storage stability due to the limitations of the process.
The suspension polymerization toner can be obtained by dispersing CCA, waxes, pigments and other components together into a monomer uniformly, and carrying out a polymerization after high-speed shearing and granulation. The CCA in the toner particles disperse more uniformly, and the particles have a better sphericity. Thereby, these particles have a good uniformity of charge distribution and transfer printing efficiency. But, most of the added charge control agent distribute in the central area of the toner particles. Since the toner is charged by the friction between the blade and the CCA on the surface of the toner, and the CCA distributing in the central area of the toner particles does not involve in the friction, there is a need to develop an effective method to improve the charge density on the surface of the toner.
Chinese Patent CN101473274 provides a toner of core-shell structure with a rigid and thin shell layer which is distributed with dense CCA formed by coating the surface of the toner core particles which is prepared by a suspension polymerization method with the charge control agent, via a polymer which is formed through a polymerization reaction of the shell monomer components. However, the method results a large amount of free CCA due to a poor compatibility of CCA and shell rein.
Chinese Patent CN101727031 provides a polymerization toner with high dense surface charges obtained by adding a reactive anionic surfactant containing a reactive functional group into an aqueous dispersant, grafting it to the surface of the toner particles by the way of polymerization. If the amount of the reactive anionic surfactants added in the method is too high, it results in fine particles in the suspension system. It also results in background pollution on the printed image. Furthermore, the high hydrophilic of the surfactant has effect upon the processes such as post-cleaning and post-process and the like.
Chinese Patent CN1707366 also provides a toner of core-shell structure including a surface layer with dense positive charges formed by polymerizing a monomer containing amine or ammonium salt on the surface of the toner core particles or salting out, melting and bonding with a polymer particle containing amine or ammonium salt. The toner core particles prepared with this method is substantially unchanged. The charging performance of the toner particles is mainly achieved by the surface layer of the particles. However, due to the efficiency of coating the surface layer of the particles, the system is easy to produce the particles with a poor charging performance even uncharged particles. Then it results in a poor printing quality.
On the other aspect, many patent applications with regard to the suspension polymerization toner provide a method of coating shell layer to improve the balance of low- temperature fixation and environmental stability of the toner particles. But coating shell layer inevitably results in that some of the CCA on the surface of the toner core particles is covered. It causes the surface of the toner particles is non-uniformly charged, which instead reduces the characteristic of surface electrification uniformity of the suspension toner.